Workpiece changer

ABSTRACT

A workpiece change for use in a machine tool that comprises a tool spindle for damping tools for machining workpieces, comprises two wheels arranged parallel to one another and rotatable about an axis of rotation into at least two prominent angular positions. Two swivel tables for clamping workpieces are arranged between the wheels and are each mounted on the wheels to swivel about a swivel axis which runs parallel to the axis of rotation. In each prominent angular position, one of the swivel tables is located in its working position in which clamped workpieces can be machined with the tools. Both wheels are supported at their rim.

RELATED APPLICATION

This is a continuation application of co-pending international patentapplication PCT/EP 2013/066883, filed Aug. 13, 2013 and designating theUnited States, which was published in German as WO 2014/029661 A1, andclaims priority to German patent application DE 10 2012, filed Aug. 23,2012, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a workpiece changer for a machine toolwith Stool spindle into which the tools can be clamped for machiningworkpieces, with two wheels which are arranged parallel to one anotherand which are rotatable about an axis of rotation into at least twoangular positions, at least two swivel tables for clamping workpieces,the swivel tables being arranged between the wheels and mounted in aswivelling manner on said wheels, each about a respective swivel axis,which swivel axis runs parallel to the axis of rotation, and wherein ineach angular position one of the swivel tables is located in its workingposition in which clamped workpieces can be machined with the tools.

2. Related Prior Art

Such a workpiece changer is known, for example, from DE 35 05 138 C2.

The known and other workpiece changer can in principle be used withvertical or horizontal tool spindles, wherein the tool spindles can bemoved relative to the workpiece changer in the three orthogonal spatialaxes X, Y and Z. Moreover, the working spindle can be mounted in aswivelling manner about one of the spatial axes.

Devices with which the workpieces to be machined are clamped arearranged on the at least two swivel tables so that they are availablefor machining.

While one of the swivel tables is in its working position, in which theworkpiece clamped on it is machined, the other swivel table is locatedin a position in which a finished machined workpiece can be removed anda new workpiece to be machined can be clamped.

Both swivel tables are each mounted in a swivelling manner between thewheels so that a clamped workpiece can point upwards both in the workingposition and in the position in which workpieces are changed. For thispurpose, it is necessary that, in the case of each change of workpiece,each swivel table is rotated 180° between the wheels.

The swivel axis of the swivel tables can furthermore be used as afurther machine axis so that, during machining of the workpieces, thesecan be provided to the tool in a different angular alignment about theX-axis.

In order to increase the flexibility of machining, the tool spindle canbe swivelled about an axis which runs transversely to the swivel axis sothat oblique machining of the workpieces is also possible from thisdirection.

In general, the three orthogonal axes are realized in the tool spindlewhich is arranged in a spindle head which is arranged, where necessaryin a swivelling manner, on a stand and is adjustably on the stand in thedirection of the longitudinal axis of the tool, i.e. the Z-axis. Thisstand enables movement in the two other spatial directions, i.e. in theX and Y direction.

It is also known in the case of machining of very long structural partsto move the workpiece changer in the direction of the swivel axes andthe axis of rotation of the wheels, i.e. in the X direction with respectto the tool spindle, i.e. to realize at least one axis in the workpiece.

When the workpiece clamped on the swivel table located in the workingposition has been machined, the wheels are rotated about the axis ofrotation by 180° so that the other swivel table is now located in itsworking position and the workpiece which has just been machined can bereplaced by a workpiece still to be machined.

For the purpose of this change of workpiece, the two wheels are rotatedsynchronously with one another about 180° so that they are rotated fromtheir first angular position, in which one swivel table is in itsworking position, into their other angular position, in which the otherswivel table is located in working position.

It is also known to equip such a workpiece changer not with two, butrather, for example, with four swivel tables so that the swivel tablesare arranged on the wheels offset with respect to one another by 90°.The workpiece changer correspondingly then has four designated angularpositions for its wheels in which in each case one of the swivel tablesis located in its working position.

Although the known workpiece changers have proved useful in manyapplications, the machine tools fitted with them are very large,particularly in cases where large structural components which also havea corresponding length in the x direction of, for example, 3 m aresupposed to be machined on them.

In particular when machining of the workpieces is supposed to be carriedwith a double spindle into which therefore two machining tools areinserted which machine the workpiece located in the working positionindependently of one another, the overall dimensions of the knownworkpiece change table are so large that a machine tool in the cabin orhousing of which the workpiece changer is set up has a very largevolume.

SUMMARY OF THE INVENTION

In view of the above, one object underlying the present invention is toimprove the known workpiece changer such that it has overall smallerdimensions and enables a quick change of workpiece while having a largeclamping surface on the workpiece tables and a structural simple design.

According to the invention, this object and other objects are achievedin the case of the known workpiece changer in that the two wheels aresupported at their rim.

The inventors of the present invention have namely recognized that amajor problem of known workpiece changers lies in the fact that, in onestructural variant, the swivel axis lies in a shaft running centrallythrough the wheels, for which purpose corresponding rotary bearings arealso provided there for the shaft.

The shaft forming the swivel axis runs between the swivel tables fromone wheel to the other in order to ensure that the two wheels arerotated synchronously which is essential for the precision of thepositioning of the swivel tables. The synchronous rotation of the wheelsfurthermore ensures that the swivel tables themselves, which are mountedrotatably on the two wheels, do not tilt or twist.

This central shaft on which the two wheels are mounted is supported incorresponding receptacles or brackets, wherein the motor for rotation ofthe wheels is provided on one of these receptacles from the outside.

This construction leads to the entire workpiece changer being overallvery wide in the x direction because, in addition to the width of theswivel tables, the width of the wheels and the motor and the twobearings for the wheels must also be taken into account.

Moreover, the shaft running centrally through the two wheels leads tothe two swivel tables having to have a specific distance to one anotherso that the interference contour of the clamped workpieces does notcollide with the central shaft during rotation of the swivel tablesabout their respective swivel axis.

In the case of other construction variants, both wheels are driven sothat, where applicable, the central shaft can be omitted, but driveswith a wide structure in the x direction are correspondingly providedfor this purpose at both wheels.

The total width of the workpiece changer could thus be reduced in thatthe or each drive motor is not arranged centrally, rather is positionedoutside of the contour of the wheel in front of the workpiece changer.However, this leads to the depth of the thus modified workpiece changerincreasing again.

The inventors of the present application have now taken a completelydifferent path by virtue of the fact they mount the two wheels on theirrim.

As a result, on one hand, the central shaft is omitted so that, in thecase of identical interference contours of the workpieces clamped on theswivel tables, the two swivel tables themselves can have a smallerdistance to one another because namely the central shaft is absent. Thisenables wheels with a smaller diameter than in the prior art.

The new workpiece changer furthermore does not require a central bearingon which the wheels are held. This again also reduces the width of theworkpiece changer in the x direction.

Moreover, the support—according to the invention—of the wheels at theirrim furthermore makes it possible to allow the rotary drive to engagedirectly on the rim what offers a large number of structuralpossibilities for positioning the rotary drive on the new workpiecechanger.

In one embodiment, each wheel has an annular guide rail which extendscentrally with respect to the axis of rotation and which runs in guideshoes which are fastened to a structural element of the machine tool,wherein the guide shoes are fastened to the structural element,preferably with an overlap angle in relation to the guide rail of lessthan 180°.

This measure is particularly structurally advantageous since only asmall region of the entire circumference of the respective wheel isrequired for the mounting so that the remaining region of thecircumference of the wheel is free of structural parts of the workpiecechanger and does not require any more space there than corresponds tothe diameter of the wheel.

The guide shoes represent as it were the bearing for the respectivewheel, wherein the guide rail is formed like a short cylinder wall thatruns externally on the circumference of the wheel and extends in thedirection of the axis of rotation.

If the annular guide rails of the two wheels point to one another, thisfurthermore means that the guide shoes and the guide rails are arrangedin the space between the two wheels what once again contributes to areduction in the width of the new workpiece changer.

According to a further embodiment, each wheel is rotatable about theaxis of rotation via a rotary drive which engages on its annularcircumferential surface, wherein each wheel may be provided with atraction means element which extends at least partially along itscircumferential surface, which traction means element interacts with adrive pinion of the rotary drive, wherein the traction means element mayfurther be fixed with both its ends on the circumferential surface ofthe wheel and may loop around the drive pinion.

A traction means element refers in the present case to an element thatis formed as a toothed belt, chain, cord, V-belt or comparable driveelement.

In the case of this measure, it is advantageous that the rotary drivealso engages directly externally on the rim of the wheels, wherein alower torque is required at the drive in order to rotate a wheelexternally on its rim than if the rotary drive were to sit directly onthe central shaft.

A traction means drive is furthermore structurally advantageous becauseit has a narrow design and is easy to mount and maintain.

Alternatively, it would also be possible to provide a spur gearingdirectly on the circumferential surface of the wheels, and drive thewheel directly via a pinion.

A traction means drive, in the case of which one end of the tractionmeans element is arranged on the circumferential surface of the wheel,and the traction means element then extends along the circumference,i.e. the circumferential surface of the wheel, then runs to a drivepinion, loops around this and goes back to the wheel, wherein the secondend of the traction means element is also fastened on thecircumferential surface, represents a structurally simple andsmooth-running drive. It may be necessary to guide the traction meanselement through under a tensioning roller in order to place it on thewheel over as large as possible a region of the circumference of thewheel, i.e. the annular circumferential surface.

In the case of this construction, in contrast to the drive via theface-side toothing, it is indeed no longer possible to rotate the wheelspermanently in one direction, but it is entirely sufficient for thechange of workpiece if the two wheels can be rotated to and fro by 180°with respect to a home position.

In one embodiment, the rotary drive has a rotary motor which drives adrive shaft on which two drive pinions sit via which the two wheels canbe driven about the axis of rotation.

This measure is also structurally advantageous since in this manner bothwheels are rotated synchronously even if, in contrast to the prior art,no central drive shaft but rather a drive shaft is provided that can nowbe arranged outside the contour of the wheels in front of or below theworkpiece changer.

This type of drive therefore does not increase the depth of the newworkpiece changer across the diameter of the wheels.

In a further embodiment, an indexing device is assigned at least to oneof the two wheels, which indexing device fixes the wheel in the angularpositions.

It is advantageous in the case of this measure that at least one of thetwo wheels is stationary in the angular positions in which in each caseone swivel table is located in its working position so that duringmachining of the workpieces the swivel tables are held in their positionby the indexing device and cannot rotate.

Particularly if the rotation of the wheels is carried out via a tractionmeans drive, the indexing device ensures in a structurally simple mannerthat the wheels cannot be rotated out of the working position.

A corresponding indexing device may be provided each of the two wheels.

In one embodiment, the indexing device comprises two onboardpositive-locking elements which are arranged on the wheel, and which areeach assigned to a working position of a swivel table, and to which isassigned a stationary positive-locking element with which the onboardpositive-locking element can be locked, the assigned swivel tablewhereof being located in its working position.

This measure ensures a structurally simple design of the indexingdevice, wherein the indexing device is also easy to adjust. Namelyeither only the onboard or the stationary positive-locking elements haveto be adjustable.

If the workpiece changer contains two swivel tables, correspondingpositive-locking elements are arranged on the wheel or wheels at twodiametrically opposite positions. These onboard positive-lockingelements swap their position in the case of each workpiece change, aretherefore also rotated back and forth by 180°.

A stationary positive-locking element is additionally provided which canbe arranged, for example, on a structural element of the machine tool.This stationary positive-locking element is arranged such that it canthen always be locked with one of the onboard positive-locking elementswhen the swivel table assigned to the respective onboardpositive-locking element is located in its working position.

The arrangement of the onboard positive-locking elements and theresultant arrangement of one stationary positive-locking element perwheel can be selected such that the indexing device is accommodated in amanner which is geometrically suitable for the workpiece changer,without noticeably impairing its width, depth or height.

The stationary positive-locking element can be arranged, for example, sothat it is displaceable in the direction of the axis of rotation of thewheels and can thus be pushed onto the onboard positive-locking elementsand locked with these when a working position of a swivel table isreached.

According to another embodiment, the indexing device further comprises alongitudinally displaceably mounted positive-locking element which canbe brought into engagement with the onboard positive-locking element,the assigned swivel table of which is located in its working position,and the stationary positive-locking element.

In the case of this measure, it is advantageous that the stationarypositive-locking element, which therefore defines the reference positionfor the working position, has not to be movable even not in thedirection of the axis of rotation, i.e. is in actual fact a stationarypositive-locking element.

The stationary or fixed positive-locking element can in this manner beadjusted with high precision in relation to the working position. In theworking position of a swivel table, the assigned onboardpositive-locking element is then located next to the stationary or fixedpositive-locking element so that the displaceably mountedpositive-locking element can then be pushed onto both positive-lockingelements, and thus lock these to one another.

If the onboard positive-locking element each is arranged externally atthe rim of a wheel, a very solid locking of the wheel in the respectiveworking positions of the swivel tables can be produced in this manner.

The positive-locking elements may be formed as gear rack segments.

It is advantageous here that as a result of the pitch of the teeth ofthe gear rack segments a very high resolution in the relative positionof the gear rack segments to one another and thus a very precisepositioning of the wheels is possible.

In one embodiment, at least at one of the two wheels an energy chain isprovided that winds on and off during rotation of the wheels about theaxis of rotation, via which energy chain the workpiece changer issupplied with energy and/or media.

This measure also ensures that the size of the new workpiece changer isreduced since it is also not necessary for the supply of electricalenergy, hydraulic oil or pneumatic air and for the transfer ofmeasurement and control signals to arrange components in the axis ofrotation of the wheels, rather the energy chain can be arranged in theexternal region of the wheel, but within its circumference, and cancorrespondingly wind on and off during swivelling to and fro of thewheels.

This measure is particularly advantageous if a swivelling drive isassigned to each swivel table, which swivelling drive is mounted on oneof the two wheels.

Because the swivel tables themselves can be formed very rigidly like acradle device, it is namely only necessary to drive the swivel tables atone end of the swivel axis, i.e. at one wheel. The swivelling drivesrequired for this purpose have a very much smaller structure than acentrally arranged swivelling drive for the entire workpiece changer sothat the swivelling drives hardly or do not noticeably impair the entirewidth of the new workpiece changer. It is also possible to integrate theswivelling drives partially in the wheels themselves.

The swivelling drives of the swivel tables are thus supplied with energyand actuated via the energy chain.

In the event that automatically actuated devices, rinsing devices,sensors, etc. are provided on the swivel tables, the swivel tablesthemselves must also be supplied with energy and media.

In view of the above, on that one wheel an energy chain which winds onor off during swivelling of the swivel tables about their respectiveswivel axis may be provided for each swivel table, via which energychain devices on the respective swivel table are supplied with energyand/or media.

At least one separating wall may be provided between the wheels, whichseparating wall separates the swivel table located in the workingposition from the at least one other swivel table.

In the case of this measure, it is advantageous that, as a result of astructural element between the swivel tables, which can be formed to bevery thin-walled, a reinforcement of the two wheels parallel to oneanother is possible which increases the precision with which the swiveltables can be positioned in working positions.

If a separating wall connected to the wheels is provided between thewheels, this ensures adequate rigidity of the swivelling devicecomprising the wheels and the swivel tables such that the two wheelsonly have to be guided at their rim across a small angle range.

The inventors of the present application have recognized that it issufficient if the wheels are guided at their rim across an angle rangeof approx. 120°, the other 240° of the rim are thus free and define, asit were, the external contour of the new workpiece changer there.

It is further advantageous here that the frame of the machine tool onlyhas to have structural elements for mounting the wheels in this region.

If, in contrast, the wheels are already sufficiently reinforced by theswivel tables and the other guidance at their rim, it is not absolutelynecessary that the separating wall is connected to the two wheels.

In this case, the separating wall can be arranged such that it onlyserves to cover the swivel table located in the working position so thatchips and drilling and cooling water which arise during machining of theworkpiece clamped there do not exit out of the working region of themachine tool and thus impair or even endanger operating personnelreplacing a machined workpiece for a blank at the other swivel table.

In one embodiment, a window is provided in at least one of the twowheels for each swivel table, through which window the swivel table canbe observed, the window preferably being mounted movably on the wheel.

In the case of this measure, it is on one hand advantageous that themachining process can be observed at all times from the outside, towhich end corresponding windows or panes are also provided in thehousing of the machine tool.

A particular advantage of the window mounted movably on the wheel liesin the fact that an intervention can be made at any time from the sideinto the working space of the machine tool so that corresponding windowsor openings in the separating wall can be omitted. In this manner, theseparating wall can be configured to be very thin which once again leadsto a reduction in the size of the new workpiece changer.

Opening of the windows on the wheel can be brought about in that thesewindows are always coupled to a window in the housing of the wheel whena swivel table is located in its working position.

A stop may be provided on the window which is movably mounted on thewheel, which stop interacts with a locking part which only allows adisplacement of the window when the wheels are located in one of theirdesignated angular positions.

It is advantageous here that the windows cannot move to and fro duringrotation of the wheels if, for example, the guides of the windows haveclearance.

According to one embodiment, the locking part is arranged in astationary manner on a housing wall and is formed as a ring against thecircumferential surface of which the stop bears during rotation of thewheels, at least one groove for the stop being provided in the ring,which groove enables a displacement of the window when the wheels arelocated in one angular position.

In this manner, a very simple locking device is produced. It is onlywhen a swivel table is located in its working position that the stoplies opposite the groove in the ring so that the window can be moved.

In view of the above, the present invention further relates to a machinetool with a tool spindle into which the tools can be clamped formachining of workpieces, the machine tool being fitted with the newworkpiece changer.

Further advantages will become apparent from the description and theenclosed drawing.

It will be obvious that the above-mentioned features which are still tobe explained below can be used not only in the respectively indicatedcombination, rather also in other combinations or on their own withoutdeparting from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are represented in the enclosed drawing andare explained in greater detail in the following description. In thedrawing:

FIG. 1 shows a schematic side view of a machine tool which is fittedwith the new workpiece changer;

FIG. 2 shows a schematic perspective view of the workpiece changer fromFIG. 1;

FIG. 3 shows a top view of the workpiece changer from FIG. 2, in aschematic representation which is not to scale;

FIG. 4 shows a view of the workpiece changer from FIG. 3 along lineIV-IV from FIG. 3;

FIG. 5 shows a view of the workpiece changer from FIG. 3 along line V-Vfrom FIG. 3;

FIG. 6 shows a view of the workpiece changer from FIG. 3 along lineVI-VI from FIG. 3;

FIG. 7 shows a sectional representation of the wheel shown in FIG. 6along line VII-VII from FIG. 6; and

FIG. 8 shows an enlarged representation of the locking element which isshown centrally in FIG. 6.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows a schematic side view, which is not to scale, of a machinetool 10 on which a tool spindle 11 is provided into which a tool 12 isclamped.

Tool spindle 11 is mounted rotatably on a spindle head 14 which ismounted in a height-adjustable manner on a moving stand 15 in thedirection of the axis of rotation of tool 12, i.e. in the Z direction.Moving stand 15 is in turn mounted displaceably on a frame 16 of machinetool 10 in the two other orthogonal spatial directions, i.e. in the Xand Y direction.

Machine tool 10 furthermore has a housing 17 which surrounds all thestructural components. In FIG. 1, housing 17 is only represented by ahousing wall 18 which is also shown broken away so that a tool magazine19 is apparent in which tools 12 can be held in available which can beexchanged into tool spindle 11, for example, using the pick-up method.

In this manner, a tool clamped into tool spindle 11 can be moved in allthree spatial directions X, Y, Z in a working space indicated at 20,into which working space a workpiece changer 21 protrudes partially inFIG. 1 from the right, which workpiece changer 21 is formed to bedrum-like.

In a manner still to be described, workpiece changer 21 is arrangedrotatably about the X-axis, which is why it is supplied via an energychain 22 with electrical energy, media and control signals.

In a manner known per se, energy chain 22 winds on and off duringrotation of workpiece changer 21 about the X-axis.

FIG. 2 shows workpiece changer 21 from FIG. 1 in a schematic,perspective representation. Workpiece changer 21 comprises two wheels 23and 24 which are rotatable about an axis of rotation 25 whichcorresponds to the X-axis from FIG. 1.

The representation in FIG 2 is such that the front wheel 23 in FIG. 1 isshown behind wheel 24 in FIG. 2.

Two swivel tables 26 and 27 are provided between the two wheels 23 and24, which swivel tables 26 and 27 can each swivel about a swivel axis 28or 29 running parallel to the axis of rotation 25.

Swivel tables 26 and 27 are formed like cradle devices, they thereforeeach comprise a flat panel 30 a with two cheeks 30, of which in FIG. 2the rear cheek is fastened to a swivelling drive 31 or 32, via whichswivel tables 26 and 27 can be swivelled to and fro at least about 180°.

FIG. 3 shows a top view of workpiece changer 21 from FIGS. 1 and 2,wheel 23 being arranged on the left in FIG. 3 in an analogous manner toFIG. 2. It is apparent in the top view of FIG. 3 that there are arrangedon panels 30 a of swivel tables 27, 28 devices 33 which serve to clampin workpieces 34 which are supposed to be machined with tools 12.

It is apparent from the comparison of FIGS. 1, 2 and 3 that lower swiveltable 27 in FIG. 3 is located outside working space 20, it is in itsexchange position in which a machined workpiece 34 can be exchanged fora blank.

In contrast to this, swivel table 27 is located in its working position36, has therefore been swivelled into working space 20 so that nowworkpiece 34 clamped on it can be machined there.

In order to be able to swivel said swivel tables 26 and 27 betweenexchange position 35 and working position 36, wheels 23 and 24 areconnected to a rotary drive 37 arranged next to and below wheels 23, 24,which rotary drive 37 has a rotary motor 38 which drives a drive shaft39 which extends parallel to axis of rotation 25.

Two drive pinions 41 and 42 sit on drive shaft 39, around which drivepinions 41 and 42 there is looped in each case a toothed belt 43 or 44which serves as a traction means element and runs in each case around anannular circumferential surface 45 or 46 of wheels 23 or 24.

For tensioning of toothed belts 43 or 44, in each case a tensioningroller 47 or 48 is arranged between wheels 23 or 24 and pinions 41 or42.

The looped arrangement of toothed belt 44 on wheel 24 is particularlyclearly apparent in FIG. 2. It is furthermore apparent from FIG. 2 thatentire rotary drive 37 is arranged quasi below the outer contour ofwheels 23, 24. In FIG. 3, for reasons of clarity, the rotary drive isrepresented outside the contour, but the spatially correct arrangementis shown in FIG. 5 which will be discussed below.

It is further apparent in FIG. 3 and in FIG. 2 than an annular guiderail 49 is provided at wheels 23 or 24 which is arranged centrally withrespect to axis of rotation 25 and has the shape of a short cylinder.

Annular guide rails 49 are as it were arranged at an rim 50 of wheels 23and 24 which are therefore mounted via their rim 50 on a structuralelement 51 of frame 16 of the machine tool as is more clearly apparentin FIGS. 1, 2 and 4.

It is furthermore apparent in FIG. 3 that an indexing device 53 isassigned to each wheel 23, 24, which indexing device 53 comprises ateach wheel 23, 24 two onboard gear rack segments 54 and 55. Each gearrack segment 54 or 55 is assigned to a swivel table 26, 27, and indeedin a crisscross manner, as is also explained below.

Each indexing device 53 further comprises a fixed, i.e. stationary gearrack segment 56 which is arranged parallel to wheels 23, 24.

FIG. 3 shows the situation in which gear rack segments 54, which areassigned to working position 36 of swivel table 27, lie in alignmentwith stationary gear rack segments 56.

In order to now lock onboard gear rack segments 54 with stationary gearrack segments 56, there is provided in each indexing device 53 alongitudinally displaceable gear rack segment 57 which can be broughtinto engagement with both gear rack segments 54, 56 via an actuatingdrive 58.

As soon as this engagement has been carried out, wheels 23, 24 areindexed, i.e. they can no longer be displaced about their axis ofrotation 25.

Gear rack segments 54, 55, 56, 57 represent an embodiment ofpositive-locking elements which can be used in indexing device 53.

If swivel tables 26, 27 are supposed to swap their positions, wheels 23,24 must be moved into their respective other angular position. For thispurpose, indexing devices 53 are initially disengaged by virtue of thefact that actuating drives 58 pull back longitudinally displaceable gearrack segments 57. Thereafter, drive shaft 39 is rotated via rotary motor38 and via this then by means of toothed belts 43, 44 wheels 23, 24 arerotated by 180° so that swivel table 26 now reaches working position 36.

In order to fix the wheels in the new angular position in a preciselypositioned and non-rotatable manner, longitudinally displaceable gearrack segments 57 now engage in onboard gear rack segments 55, which areassigned to the working position of swivel table 26, and in stationarygear rack segments 56.

Swivel tables 26, 27 must be swivelled about their swivel axes 28, 29simultaneously with the rotation of wheels 23 and 24 so that workpieces34 in FIG. 3 point upwards again.

It is furthermore apparent in FIG. 3 that a reinforcing separating wail59 is provided between the two wheels 23, 24, which separating wall 59has a very small thickness 60 so that swivel axes 28, 29 can have adistance A to one another which is merely caused by the interferencecontours of workpieces 34 and the dimensions of swivel tables 26, 27.

In this manner, the external dimensions of new workpiece changer 21 inthe direction of the Y direction from FIG. 1 are limited to diameter Dof wheels 23, 24, as is apparent in particular from FIG. 1.

Width B of the device is substantialiy determined by the distance ofwheels 23, 24 to one another, indexing device 43 and rotary drive 37only make an unnoticeable contribution to width B. as is apparent fromFIG. 2.

FIG. 4 shows the machine tool from FIG. 3 in a view along IV-IV fromFIG. 3. Wheel 24 is mounted with its annular guide rail 49 on a bentstructural element 51 which covers wheel 24 with an overlap angle 61which is significantly smaller than 180°. In the present case, theoverlap angle is approx. 120 .

By way of example, five guide shoes 62 are shown on structural element51, in which guide shoes 62 annular guide rail 49 is mounted which iscovered by guide shoes 62 as a result in overlap angle 61.

Structural element 51 has a semi-circular recess 63 which points towardsaxis of rotation 25 of wheel 24. In this manner, the majority of thesurface of wheel 24 is not covered by structural element 51.

Wheel 24 along line X-X from FIG. 3 is represented schematically in FIG.5. It can be inferred from the representation of FIG. 5 that tensioningroller 48 and drive pinion 42 are arranged, as it were, below wheel 24,i.e. within its diameter D. It is furthermore apparent that toothed belt44 is arranged with its first end 65 and its second end 66 via afastening means 67 on circumferential surface 46 of wheel 24.

In this manner, it is possible to rotate wheel 24 out of the positionshown in FIG. 5 by 180° in an anticlockwise direction about axis ofrotation 25, and correspondingly naturally also rotate it back.

As already mentioned, swivel tables 26, 27 are also rotated to and froin each case by 180° together with the rotation of wheels 23, 24 by±180°, wherein the swivel tables can be swivelled even while they arelocated in their working position 36 in order to enable machining ofworkpieces 34 at an oblique angle.

The energy supply of swivelling drives 31, 32 is carried out via energychain 22 which is apparent in FIG. 1, wherein FIG. 1 shows two furtherenergy chains 68, 69 which do not serve to supply swivelling drives 31,32, rather to supply devices 33 on swivel tables 26, 27.

FIG. 6 shows a top view of wheel 24 along line VI-VI from FIG. 3.

Wheel 24 is provided with two displaceable windows 71, 72 which aremounted movably between guides 73 and 74 or 75 and 76.

An annular locking part 77 is provided between guides 74 and 75, whichlocking part 77 interacts with two stops 78, 79 which are provided onwindows 71 or 72.

As is apparent from the sectional representation in FIG. 7 along lineVII-VII from FIG. 6, locking part 77 is arranged on housing wall 18which is only shown broken away in FIG. 1. Locking part 77 is formedhere as a ring, but can also be formed as a disc.

In the position shown in FIGS. 6 and 7, stops 78, 79 lie at the heightof grooves 81, 82 in locking part 77 so that windows 71, 72 can bedisplaced in guides 73, 74, 75, 76. However, as soon as wheel 24 hasonly rotated slightly about its axis of rotation 25, stops 78, 79 lie ona circumferential surface 83 of locking part 77 so that windows 71, 72cannot be displaced and are not displaced by themselves as a result oftheir weight when wheels 23, 24 are rotated.

Therefore, what is claimed is:
 1. A workpiece changer for use in amachine tool that comprises a tool spindle for clamping tools formachining workpieces, said workpiece changer comprising two wheels whichare arranged parallel to one another and which are rotatable about anaxis of rotation into at least two prominent angular positions, said twowheels being supported at their rim, and at least two swivel tables forclamping workpieces, the swivel tables being arranged between said twowheels and being each mounted on said two wheels such as to swivel abouta swivel axis, which swivel axis runs parallel to the axis of rotation,wherein in each prominent angular position one of the at least twoswivel tables is located in its working position in which clampedworkpieces are machined with the tools.
 2. The workpiece changer ofclaim 1, wherein each of said two wheels comprises an annular guide railextending centrally with respect to the axis of rotation and running inguide shoes which are fastened to a structural element of the machinetool.
 3. The workpiece changer of claim 2, wherein said guide shoes arefastened to the structural element such that they extend over an overlapangle in relation to the guide rail of less than 180°.
 4. The workpiecechanger of claim 1, wherein each of said two wheels comprises an annularcircumferential surface and a rotary drive is provided that engages onsaid annular circumferential surface of each of said two wheels, suchthat each of said two wheels is rotatable about said axis of rotationvia said rotary drive.
 5. The workpiece changer of claim 4, wherein eachof said two wheels is provided with a traction means element whichextends at least partially along said circumferential surface of saidwheel, said traction means element interacting with a drive pinionprovided at said rotary drive.
 6. The workpiece changer of claim 5,wherein each traction means element comprises two ends, each of said twoends being fixed to said circumferential surface of the respectivewheel, said traction means element running around and engaging the drivepinion.
 7. The workpiece changer of claim 4, wherein said rotary drivecomprises a rotating motor and a drive shaft operatively connected tosaid rotating motor, two drive pinions being arranged at said driveshaft, each one drive pinion operatively connected to one of said twowheels for rotation thereof about said axis of rotation.
 8. Theworkpiece changer of claim 1, wherein an indexing device is provided andassociated to at least one of said two wheels for fixing said at leastone wheel in the prominent angular positions.
 9. The workpiece changerof claim 8, wherein said indexing device comprises two onboardpositive-locking elements arranged on one of said two wheels, eachonboard positive-locking element being associated to a working positionof a swivel table, a stationary positive-locking element being providedand associated with said onboard positive-locking elements such as tolock the onboard positive-locking element associated to a swivel tablewhich is located in its working position.
 10. The workpiece changer ofclaim 9, wherein the indexing device comprises a longitudinallydisplaceable positive-locking element for simultaneous engagement withthe stationary positive-locking element and that onboardpositive-locking element, the assigned swivel table of which is locatedin its working position.
 11. The workpiece changer of claims 1, whereinan energy chain is provided at least at one of the two wheels, saidenergy chain winding on and off during rotation of said two wheels aboutthe axis of rotation, via which energy chain the workpiece changer issupplied at least with one of energy and media.
 12. The workpiecechanger of claims 1, wherein each a swivelling drive is provided for andassociated to each of said at least two swivel tables, each swivellingdrives being mounted on a first of said two wheels.
 13. The workpiecechanger of claim 12, wherein on said first of said two wheels each anenergy chain is provided for each of said at least two swivel tables,each energy chain winding on or off during swivelling of the respectiveswivel table about its respective swivel axis, via which energy chaindevices provided on the respective swivel table are supplied at leastwith one of energy and media.
 14. The workpiece changer of claim 1,wherein at least one separating wall is provided between the two wheels,which separating wall separates the swivel table located in workingposition from the others of the at least two swivel tables.
 15. Theworkpiece changer of claim 14, wherein the at least one separating wallis connected to both of said two wheels and reinforces the workpiecechanger.
 16. The workpiece changer of claim 1, wherein for each swiveltable a respective window is provided in at least one of the two wheels,each window enabling visual inspection of the respective swivel table.17. The workpiece changer of claim 16, wherein each window is mounted onthe wheel such as to be displaceable.
 18. The workpiece changer of claim17, wherein on each window a stop is provided which interacts with alocking part which only allows a displacement of the window when the twowheels are located in a prominent angular position.
 19. The workpiecechanger of claim 18, wherein the locking par is arranged stationary on ahousing wall.
 20. The workpiece changer of claim 19, wherein the lockingpart is formed as a ring device having a circumferential surface againstwhich the stop bears during rotation of the two wheels, at least onegroove being provided in the ring device, into which groove the stopenters when the two wheels are located in a prominent angular positionsuch as to enable displacement of the window.
 21. A machine toolcomprising a tool spindle for clamping tools for machining ofworkpieces, and a workpiece changer, said workpiece changer comprisingtwo wheels which are arranged parallel to one another and which arerotatable about an axis of rotation into at least two prominent angularpositions, said two wheels being supported at their rim, and at leasttwo swivel tables for clamping workpieces, the swivel tables beingarranged between said two wheels and being each mounted on said twowheels such as to swivel about a swivel axis, which swivel axis runsparallel to the axis of rotation, wherein in each prominent angularposition one of the at least two swivel tables is located in its workingposition in which clamped workpieces are machined with the tools. 22.The workpiece changer of claim 21, wherein each of said two wheelscomprises an annular guide rail extending centrally with respect to theaxis of rotation and running in guide shoes which are fastened to astructural element of the machine tool.
 23. The workpiece changer ofclaim 22, wherein said guide shoes are fastened to the structuralelement such that they extend over an overlap angle in relation to theguide rail of less than 180°.
 24. The workpiece changer of claim 23,wherein each of said two wheels comprises an annular circumferentialsurface and a rotary drive is provided that engages on said annularcircumferential surface of each of said two wheels, such that each ofsaid two wheels is rotatable about said axis of rotation via said rotarydrive.
 25. The workpiece changer of claim 24, wherein said rotary drivecomprises a rotating motor and a drive shaft operatively connected tosaid rotating motor, two drive pinions being arranged at said driveshaft, each one drive pinion operatively connected to one of said twowheels for rotation thereof about said axis of rotation.
 26. Theworkpiece changer of claim 25, wherein an indexing device is providedand associated to at least one of said two wheels for fixing said atleast one wheel in the prominent angular positions.
 27. The workpiecechanger of claim 21, wherein at least one separating wall is providedbetween and connected to both the two wheels to reinforce the workpiecechanger, which separating wall separates the swivel table located inworking position from the others of the at least two swivel tables.